1. Field of the Invention
This invention relates to a piezoelectric device, more particularly to a piezoelectric device having a nanoimprinted film.
2. Description of the Related Art
A ferroelectric polymer material, such as poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE), can be treated to exhibit piezoelectric property.
US 2009/0047445 A1 discloses a method of forming a piezoelectric device by the steps of: heating a piezoelectric precursor (such as PVDF-TrFE) to a temperature that is above a Curie temperature of the precursor, but below a melting temperature of the precursor; applying a voltage across the precursor; and reducing the temperature to below the Curie temperature while the voltage is applied.
Chien-Chong Hong (joint inventor of the present invention) et. al proposed a method of nanoimprinting a piezoelectric polymeric material for forming high aspect ratio nanopillars in U.S. application publication no. 2012/0276333 A1. The method includes heating a surface of the piezoelectric polymeric material to a temperature less than a Curie point of the polymeric material by not more than 25° C., and pressing the heated surface of the material using a nanoimprinting template such that the piezoelectric polymeric material is formed with nanopillars.
In an article entitled “Enhanced Piezoelectricity of Nanoimprinted Sub-20 nm Poly(vinylidene fluoride-trifluoroethylene) Copolymer Nanograss,” 2012 American Chemical Society p 1580-1586, Chien-Chong Hong (joint inventor of the present invention) et al. further proposed poling the nanopillars of the piezoelectric polymeric material in an electric field and at an elevated temperature.
In is known in the art that, to obtain a piezoelectric material with better piezoelectric response, the most effective way is to apply an electric field (i.e., applying a voltage) across the piezoelectric material to reverse dipole moments of molecules in the material. However, such approach may result in undesirable breakdown of the piezoelectric material.